Field of the Technology
The current invention relates to the field of gyroscopes, specifically methods of improving the long term in-run bias stability of Coriolis vibratory gyroscopes.
Description of the Prior Art
The level of long term instability of bias and scale factor are key characteristics defining the utilization of gyroscopes in many practical applications, including navigation, positioning, and targeting systems. Thermal sensitivity of system's components accounts for the first order drift mechanisms of gyroscopes. Thermal variations are typically identified and calibrated by utilizing the linear dependence of the gyroscope bias on the drive-mode resonant frequency. This approach, however, only captures the thermal drift of the mechanical parameters, as reflected in the mechanical resonant frequency of the device. The thermal sensitivity of other system components, such as electronic gains, remains unobservable.
The level of long term instability of bias and scale factor are key characteristics defining the utilization of gyroscopes in many practical applications, including navigation, positioning, and targeting systems. Thermal sensitivity of system's components accounts for the first order drift mechanisms of gyroscopes.
Thermal variations are typically identified and calibrated by utilizing the linear dependence of the gyroscope bias on the drive-mode resonant frequency. This approach, however, only captures the thermal drift of the mechanical parameters, as reflected in the mechanical resonant frequency of the device. The thermal sensitivity of other system components, such as electronic gains, remains unobservable.
The thermal drifts of the electronic components for the drive-mode can be avoided by using the Side Band Ratio (SBR) method. The SBR algorithm takes advantage of the non-linearity of parallel-plate sense capacitors, allowing a direct measurement of large mechanical amplitudes. This direct measurement of mechanical amplitude can be used by a type of amplitude gain control (AGC), for the purpose of creating a steady-state mechanical amplitude of the resonator. In response to this amplitude, the AGC creates an AC signal, possibly then mixing it with a DC signal, and feeding the result back into the resonator as a forcing function. Modification to both the AC and DC control voltages can also be used for the purpose of resonator control. This method can only be applied to the drive-mode, leaving the drift in sense-mode electronic components unobservable. Thus, there is a need to find a method of capturing the bias drift of the sense mode, which can be a combination of both thermal drift in the pick off components, or other sources of bias drift as well, such as due to acceleration or aging of the device. Compensation of these effects can increase long-term stability of both in-run bias and scale factor.
What is needed is an algorithm that incorporates the quadrature signal for the in-run calibration of bias. Quadrature is typically considered a parasitic signal in gyroscopes which distorts the rotation-induced response of the sensor. It is preferred that a quadrature signal could be utilized for compensation of thermal drift in sense mode detection system. Variations in the quadrature signal should also be used to compensate for the parasitic-induced rotation response, thus minimizing the influence of thermal drift in electronics.